How to sell a software application online?

I have developed a software application that I wish to sell online. A web site has been designed and hosted to sell it. The sales of this program are likely to be modest and take place over a period of about 2 to 4 years. It is a niche product, there is probably no mass-market opportunity. There will likely be no other products for sale. I have chosen a name for a company to sell the software program - am assuming this is obligatory? So far it is just a name I invented, there is no legal structure for such a company in France.

I have chosen a company in the US called FastSpring to handle the e-commerce payments. They work as wholesalers and take care of TVA tax world wide. They simply take a percentage, send the rest to any bank accounts nominated. My questions revolve around the simplest, quickest, best way to get a company up and running to begin sales and the requirements around the names of the application and of the company.

There are minimal continual development costs and expenses. Some web site development costs as I don’t do the actual site, just the software. The profits will be distributed between myself and a person in charge of marketing. The distribution takes place at FastSpring, who will send a certain percentage to each of us in France if we can set up something reasonable here.

Questions:

1. Must the product name and/or company name be trademarked or protected in some way?
2. If so, should the trademark(s) be international?
3. How to do a trademark name search on our own and file without a lawyer?
4. Of the legal structures in France, auto-entrepreneur, etc., what is the simplest, best, structure one can use to sell a software program online?